I. Field of the Invention
This invention relates to electrical and fiber optic cable mounting and protection. More particularly, the present invention relates to a method and apparatus for routing electrical and fiber optic cables through and sealing across enclosure bulkheads typically located in outdoor environments.
II. Description of the Related Art
Many electrical or electromechanical assemblies are housed inside enclosures to protect them against the environment or certain environmental conditions in which they are located. Frequently, these assemblies require electrical signals from external sources for their operation and/or need to provide signals to other devices located outside of the enclosure. Such signals are often transferred using electrical or fiber optic cables. The cables or conductors must be passed through a wall of the enclosure in order to interface with the electrical/electro-magnetic assembly inside or other devices outside.
Typically, one or more apertures are formed through a wall of the enclosure to allow cable access to the electrical assembly inside. Each aperture, or access hole, must be large enough in area to pass a corresponding cable and sometimes a cable-mounted connector.
Several problems result from forming the access holes. In the case of a metal enclosure, sharp edges may result from forming the access holes which can cut through the cable's insulation, shorting out the electrical signal carried by one or more center conductors. Another problem is that the access holes allow moisture, dirt, and other contaminants inside the enclosure which can damage the electrical components inside.
To combat these problems, rubber grommets have been used to protect the cables from the sharp metal edges of the access holes. A grommet can be mounted around an access hole to provide a non-abrasive surface against which a cable may rest. The grommets are inexpensive, easy to install, and work quite well at preventing cable damage due to chaffing. However, the inside diameter of the grommet must be large enough to allow sufficient clearance for the cable and connector. Typically, the connector diameter is much larger than the cable diameter so that once the cable is installed through the access hole and grommet, a gap remains between the cable outer surface and the grommet inner surface. This gap allows moisture and dirt to penetrate the enclosure which can result in damage to the assembly or components inside. Additionally, the gap permits the cable to move in applications where vibration is prevalent, which may damage the cable or degrade the electric or fiber optic signals therein.
To eliminate the gap between the inner grommet surface and the cable jacket, a second type of rubber grommet has been developed. This grommet is described in U.S. patent application Ser. No. 08/889,347, entitled "SLIDING GROMMET," which is incorporated by reference herein. This type of grommet comprises a bell-shaped housing as part of a typical O-shaped grommet, mounted to an access hole in a wall. The bell-shaped housing protrudes from the wall or surface to which it is mounted at a fixed angle, typically 45 or 90 degrees. A cable is fed through the bell-housing and access hole, and is then connected to a mating connector inside the enclosure. Finally, a plug is installed around the cable and brought toward the bell-shaped housing, where it is inserted and secured in place with a tie-wrap or other suitable device.
One problem that results from using the bell-shaped grommet described above is that the angle of the cable protruding from the enclosure is somewhat fixed, especially if an environmental seal is achieved by the grommet. Often it is desirable to alter the cable mounting angle with respect to the enclosure surface. Using a bell-shaped grommet as described above, an attempt to alter the cable position or routing can unseat the housing, allowing exposure of the enclosure interior to outside contaminants. The housing may also become dislodged due to vibration or sudden movements which are typical in mobile applications.
An additional problem which results when using conventional or bell-shaped grommets is the decreased bend radius that results from a sharp mounting angle, shown in FIG. 1a. In many applications, the cable is installed into a cramped environment, forcing a bend radius smaller than the cable is designed to withstand. This is especially a problem with fiber optic cables. The problem is lessened somewhat by the use of an angled bell-housing, as shown in FIG. 1b, however, the cable mounting angle is fixed and unable to be altered, if needed.
What is needed is a grommet which provides a weatherproof cable interface to an enclosure, while enabling maximum cable movement and a variable mounting angle relative to the enclosure surface.